1. Field of the Invention
This invention relates to a light-emitting device, more particularly to a light-emitting device including a substrate formed with a recess, and a continuous heat-dissipating layer formed on the substrate.
2. Description of the Related Art
FIG. 1 illustrates a conventional light-emitting diode that includes a sapphire substrate 11 having an epitaxial-forming surface 111 and a back surface 112 opposite to the epitaxial-forming surface 111, an epitaxy layer 12 formed on the epitaxial-forming surface 111, and a pair of electrodes 131, 132 coupled to the epitaxy layer 12.
When electricity is applied on the epitaxy layer 12 of the light-emitting diode, light resulting from electron-hole pairs in the epitaxy layer 12 will be generated. However, nearly 70% of light generated in the diode is converted into heat, thereby causing a junction temperature of the light-emitting diode to increase, which results in a decrease in radiative recombination efficiency of the light-emitting diode. In general, the sapphire substrate 11 is attached to an aluminum board 150 through a silver paste 140. Since the aluminum board 150 has a relatively large area, heat generated in the diode can be dissipated quickly therefrom, thereby permitting lowering of the junction temperature of the light-emitting device. Since the heat generated in the diode is dissipated through the sapphire substrate 11 to the aluminum board 150, and since the sapphire substrate 11 has a thick layer thickness and a relatively low thermal conductive coefficient, heat dissipation of the diode is still insufficient.
FIG. 2 illustrates a diode modified from the diode of FIG. 1. In this diode, the sapphire substrate 11 is removed through wafer bonding techniques, and the epitaxy layer 12 is directly attached to a silicon substrate 120 having a relatively high thermal conductive coefficient, which can improve heat dissipation of the light-emitting device. However, crystal defects propagating in the epitaxial layer 12 and resulting from a high stress applied on the light-emitting device can occur during removal of the sapphire substrate 11.